Brief heat shock affects the permeability and thermotolerance of an in vitro blood-brain barrier model of porcine brain microvascular endothelial cells.

Heat shock was imposed on an in vitro model of the blood-brain barrier (BBB) by submersion into prewarmed growth medium. Transendothelial electrical resistance (TEER) was used to assess the functional integrity of the endothelial barrier. Consequences of the heat shock were highly dependent upon the temperature and duration of exposure. Temperatures below 47 degrees C required more than 30 s of exposure to significantly impair barrier function, but full recovery occurred within 1 h. When the temperature was 50-54 degrees C, an exposure of only 10 s significantly diminished barrier function. Ten seconds of 51 degrees C or 54 degrees C caused a significant loss of barrier function (45% and 80%, respectively). Full recovery from the 51 degrees C shock occurred within 5 min, while recovery from the 54 degrees C shock required more than 10 h. When the temperature was 57 degrees C or greater, a 3-s duration diminished barrier function by 80%. In response to heat shock, the brain microvascular endothelial cells developed thermotolerance and over-compensated in their ability to form a physiological barrier. The BBB models lost more than 60% of barrier function when initially exposed to 53 degrees C for 5 s but lost only 30% of function when exposed to the same treatment 24 h later. The BBB models over-compensated to produce a reinforced barrier with double the original TEER following repeated application of heat treatment (57 degrees C for 3 s). In vivo experiments will require exquisite manipulation of the temperature and duration in order to achieve the desired opening of the BBB in therapeutic applications.